1. Technical Field
The present invention relates to an electroluminescent device.
2. Related Art
From the viewpoint of reducing weight, thickness, and power consumption, electroluminescent devices have been developed actively, such as a display and an exposure head that include an organic electroluminescent element for each pixel. Such an organic electroluminescent element (hereinafter referred to as organic EL element) generally has the structure in which a luminescent layer made of an organic material is disposed between two electrodes. For a display or the like, such an organic EL element constitutes a pixel and a plurality of pixels are arranged in a matrix manner on a substrate. For an active matrix light-emitting device, thin film transistors (TFTs) are provided on the substrate to control driving current applied to the organic EL elements, and a planarizing layer is formed over the TFTs. The organic EL elements are disposed on the planarizing layer.
The organic EL element is liable to be degraded by water. Specifically, if water permeates the organic EL element the material of the luminescent layer may be altered, or the luminescent layer may separate from the electrode (cathode) and consequently carriers (electrons) are not supplied to the luminescent layer from the cathode. As a result, a so-called dark spot is produced, where part or the entirety of the pixel cannot emit light all the time. If the planarizing layer contains water, the water is heated by heat from the TFTs and the luminescent layer, and the water transfers from the planarizing layer and permeates into the luminescent layer through the electrode, so that a dark spot is undesirably produced.
Accordingly, for example, Japanese Unexamined Patent Application Publication No. 2003-297551 has disclosed a structure in which a moisture-proof inorganic barrier layer is formed of silicon oxynitride over the entire surface of the planarizing layer at the organic EL element side to prevent water from permeating into the organic EL element from the planarizing layer.
However, even in the structure disclosed in the above-cited document, in which the inorganic barrier layer is formed over the entire surface of the planarizing layer, if a defect such as a pinhole is formed in the inorganic barrier layer, water can undesirably permeate into the organic EL element through the defect.